Further tweaks for comment-start-skip behavior
* lisp/newcomment.el (comment-normalize-vars): Only add escaping check
to `comment-start-skip' if not `comment-use-syntax'.
(comment-beginning): Use `narrow-to-region' instead of moving back
one character.
(http://lists.gnu.org/archive/html/emacs-devel/2014-03/msg00488.html)
(comment-start-skip): Update the docstring.
Fixes: debbugs:16971